Adapt a Waveblaster soundcard to the ST

The PC-world is filled with simple things with fancy names, and
Waveblaster is one of them. It's a impressive sounding name for a
impressing sounding technology from Creative Labs, but in reality it's
nothing but a combined MIDI- (crippled ofcourse, this is PC-
technology) power- and audio-connector. The purpose of the
Waveblaster-port (which is present on most/all Soundblaster-cards and
-clones) is to connect a daughterboard with proper MIDI-sound. By
building a Waveblaster-port yourself you can connect these cards to
your ST/Falcon/whatever.

What do you need?

A computer with a standard MIDI interface.

A PSU that can deliver +5v, +12v and -12v.

A piece of Veroboard or similar, some cheap parts.

Some experience with a soldering iron.

A Waveblaster MIDI-card.

Point 2 will probably cause a few headaches, as the standard PSU in the
(Mega)ST/Falcon doesn't have -12v. I have been informed that the TT- and
MegaSTE-PSU will deliver -12v. You'll also need some space for the card, so
this project is probably best suited for those of you that have recased
machines with PC-powersupplies.

It's also possible to convert a Waveblaster-card into a complete standalone
MIDI-unit (Elektor Electronics, July/August 1997), but buying a ordinary GM/XG
module is probably cheaper.

Pin-layout

This is the layout of the Waveblaster port:

Waveblaster pin-layout

2,4,6,8,10,12,16,18,20,22,24,26: Ground

3: MIDI in

The MIDI-input is TTL, so you'll need some circuitry to convert the
standard MIDI current loop to TTL.

14,1,7,11,15: Not connected

5,9,13: +5V

17: +12V

21: -12V

19: Audio out, right

23: Audio out, left

The audio-outputs are standard line-level, but can't deliver enough
juice for headphones.

25: Reset

Reset is active low.

The complete circuit

This circuit has everything you need to connect a Waveblaster-card to your
ST/Falcon. It consists of three main-parts:

MIDI "current loop" to TTL converter

The optocoupler IC1 with the additional parts D1, R4 and R5 converts
MIDI "current loop" to TTL. This is cruical, I tried several solutions
before I resigned and ordered myself some optocouplers.

Buffer and MIDI-THRU

IC2 buffers the converted TTL-signal before it's fed to the
Waveblaster-port, as well as providing a MIDI-THRU together with R2 and
R3. MIDI-THRU must be used as your machine's new MIDI OUT if you need
one.

Reset

R1/C6 resets the card at power-up. You could replace C6 with a switch
and reset manually, but I wouldn't recommend that as the card can easily
be reset by software if needed.